Title: SUBGRADE CHARACTERIZATION FOR HIGHWAY PAVEMENT DESIGN
Abstract: Subgrade soil characterization expressed in terms of Resilient Modulus (M sub R) has become crucial for pavement design. For a new design, M sub R values are generally obtained by conducting repeated triaxial tests on reconstituted/undisturbed cylindrical specimens. Because of the complexities encountered with the test, in-situ tests would be desirable, if reliable correlation can be established. In evaluating existing pavements for rehabilitation selection, subgrade characterization is even more complex. The main focus of this study is to determine subgrade M sub R employing a Dynamic Cone Penetrometer (DCP), especially the automated version. In support of the study, side-by-side Falling Weight Deflectometer (FWD) tests are also conducted. Twelve as-built test sections reflecting typical subgrade soil materials of Mississippi are selected and tested with DCP and FWD before and after pavement construction. Undisturbed samples are extracted using a Shelby tube, and tested in repeated triaxial machine for M sub R. Other routine laboratory tests are conducted to determine physical properties of the soil. In analyzing the data, the soils tested are categorized into two groups, fine- and coarse-grain soils. DCP results (DCP index, penetration/blow) from tests conducted directly in the prepared subgrade are employed to develop regression models for laboratory M sub R prediction. The predictability of the model is substantiated by repeating DCP tests at an independent site. Models for in-situ modulus prediction are also developed in the study. Deflection measurements facilitated the calculation of in-situ modulus, for which three programs were used: MODULUS 5, FWDSOIL and UMPED. The MODULUS 5 backcalculated subgrade modulus shows good agreement with the laboratory M sub R. The FWDSOIL backcalculation program predicts subgrade moduli which are slightly lower than the laboratory M sub R. With emplacement of pavement structure (lime treated subgrade, lime fly ash subbase, and several inches of asphalt concrete) atop the subgrade, the subgrade backcalculated moduli are enhanced, coarse-grain soil showing a larger increase than the fine-grain soil. This latter result, namely the enhancement of subgrade moduli, is substantiated employing the data compiled from 20 Long Term Pavement Performance (LTPP) pavement sections in Mississippi. In order to analyze the automated DCP results, a software designated Dynamic Cone Penetrometer ANalysis (DCPAN), has been developed. With the regression equation incorporated in the software, real time laboratory as well as backcalculated subgrade modulus calculations are plausible in the field.
Publication Year: 2000
Publication Date: 2000-12-01
Language: en
Type: article
Access and Citation
Cited By Count: 40
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